Chemistry-C1

Additives - make food better

Food colours - looks more appetising
Flavour enhancers - bring out taste and smell of food
Antioxidants - help preserve food
Emulsifiers - help oil and water blend together

Emulsifiers are made of droplets:
HYDROPHILLIC head - likes water
HYDROPHOBIC tail - likes oil (phobia of hydro, doesn't like water)

These droplets are made up of one liquid suspended in another

Foods cooked because:
1) Better taste and texture
2) Kill microbes that cause disease
3) Poisonous when raw
4) Easier to digest

Cooking causes CHEMICAL CHANGE - irreversible

Eggs and meat:
Protein molecules change shape when heated, cooking breaks down some chemical bonds which allows protein to change shape - gives food a more edible texture - protein becomes denatures

Potatoes:
Each potato cell has a cell wall made of cellulose, humans can't digest cellulose. Cooking ruptures the cells walls making it digestable, also makes starch grains swellup and spread out making potato softer

Baking powder:
When heated undergoes THERMAL DECOMPOSITION
Thermal decomposition - when a substance breaks down into simpler substances when heated

sodium hydrogencarbonate --> sodium carbonate + carbon dioxide + water

2CaHCO3 --> Na2Co3 + CO2 + H2O

Natural or artificial?

Chemicals that smell nices are used in perfumes and air fresheners - esters are often used
Esters are also common in nature, fuits and flowers contain natural esters
Esters can also be manufactured synthetically

Esterification:
Acid + Alcohol --> Ester + Water
-Acid is the catalyst 

Making a good perfume:

Easily evaporates - people need to smell it
Non-toxic - needs to be safe to use
Doesn't react with water - not react with sweat
Non irritable - need to be able to apply directly to skin
Insoluble in water - needs to last

Testing perfumes

Testing perfumes on animals has been banned in the EU
Perfumes have to be tested to make sure they're safe for use 

SOLIDS:
-Strong forces of attraction between patricles
-Particles don't move from regular lattice arrangement so keep fixed position
-Particles vibrate, hotter solid means more vibration

Heating - solid will melt and become liquid

LIQUIDS:
-Some force of attraction but free to move past each other
-Don't keep a definite shape, flow to fill bottom of container
-Constantly moving with random motion, hotter liquid means faster movement

Heating liquid - liquid will boil and become gas

GASES:
-Next to no force of attraction, free to move and travel in straight lines
-Only interract when they collide
-Don't keep a definite shape or volume, will always fill any container
-When they bounce off a wall they exert a pressure on the walls
-Particles move constantly with random motion, hotter gas means faster movement

Volatility - how easily a liquid evaporates
When a liquid is heated heat energy makes the particles move faster but some particles move faster than others. Fast moving particles at the surface will overcome forces of attraction and escape (evaporation)
Evaporated particles are then drifting about in the air and picked up by smell receptors so you smell it
Perfumes need to be volatile so that they evaporate enough to smell them therefore particles in perfumes have very weak attractions so it's easy for particles to overcome the attraction and escape 

Solvent - liquid that it's dissolved into
Solute - substance being dissolved
Solution - mixture of a solute and solvent 
Soluble - it will dissolve
Insoluble - it won't dissolve
Solubility - measure of how much will dissolve 

Nail varnish is insoluble in water because:
1) molcules of nail varnish are strongly attracted to each other which is stronger than the attraction between nail varnish molecules and water molecules
2) water molecules are strongly attracted to each other, stronger than attraction between water and varnish

Nail varnish is soluble in acetone because:
Attraction between acetone molecules and nail varnish molecules is stronger than the attractions holding the two substance together  

PIGMENTS - give paints their colour
Paints usually contain : solvent, binding medium and pigment
BINDING MEDIUM - carries the pigment and holds them together, sticks pigments to surface
SOLVENT - thins the paints and makes it easy to spread

PAINT = COLLOID = tiny particles dispersed in another substance (NOT mixed in with)
The tiny particles can be bits of solid, droplets of liquid or bubbles of gas
Colloids don't seperate out because the particles are so small
Paint is a colloid where PIGMENTS are dispersed through a LIQUID

WATER-BASED PAINTS: EMULSION
-Solvent used is water, binding medium is usually an acrylic
-Water-based emulsion dries when solvent evaporates, leaving behind binder and pigment as thin solid film
-Dries quite quickly
-DON'T produce harmful fumes
-Ideal for inside walls

OIL-BASED PAINTS: GLOSS
-Solvent is an organic compound that dissolves in oil, binding medium is oil
-Dries in two stages:
1) solvent evaporates
2) oil is oxidised by oxygen in air before turning solid
-Longer to dry
-Glossy, waterproof and hard-wearing
-Produce harmful fumes
-Ideal for outside doors and metal works 

Thermochromatic pigments - change colour when heated
Different pigments change colour at different temperatures, a mixture of different pigments can be used to make a colour-coded temperature scale
Often used in baby products to indicate when food or bath water is too hot
Used on kettles, mugs and mood rings

Mixing thermochromatic pigments with paint:

Thermochromatic pigments can be mixed with acrylic pain giving a wide range of colours, these paints are used on mugs so the pigment goes transparent when heated revealing a picture

Phosphorescent pigments - glow in the dark
Phosphorescent pigments absorb natural or artifical light and store the enegy
Energy is released as light over a period of time
Used in watches, clocks, traffic sign, emergency exit signs and novelty decortions

Glow in the dark watches used to be made with redioactive paints but they weren't very safe and could give off atomic radtions
Phosphorescent pigments were developed as a safe alternative 

Polymers - long chain molecules (plastic)
Made up of monomers that join together - polymerisation

Addition polymers - made from UNSATURATED monomers
Made up of DOUBLE COVALENT BONDS
Molecules with at least one double covalent bond between carbon atoms are unsaturated
Molecules with no double covalent bonds are saturated
Lots of unsaturated monomers can open up their double bonds to form polymer chains - addition poylmerisation
Name of monormer is just the normal name, eg. propene with poly added to it eg. polypropene

Different polymers have different properties:
-Strong, rigid polymers such as high density polyethene are used to make plastic milk bottles
-Light, stretchable polymers such as low density polyethene are used for plastic bags and squeezy bottles
Low density polymers have a low melting point so no good for anything that gets hot
-PVC is storng and durable but can be made either rigid or stretchy, rigid kind is used for window frames and piping and the stretchy kind is used for synthetic leather
-Polystyrene foam is used in packaging and for dispoable cups because trapped air in foam is a good insulator

Polymers in clothes:
-Nylon is often used to make clothes, they're not waterproof on their own but with polyurethrane make tough, hard-wearing, waterproof outdoor clothing
One major problem with polyurethrane is that it doesn't let water vapour pass through it so sweat condenses on the inside of the clothing - material isn't breathable
-Gore-tex materials are made by laminatiing a thin film of plastic called expanded PTFE onto a layer of another fabric (polyester or nylon) to make PTFE sturdier
PTFE has tiny holes which let water vapour through so its breathable but it's waterproof as holes aren't big enough to allow water through, and PTFE repels water

Non-biodegradable plastics:
Most plastic aren't biodegradable - don't get broken down by micro-organisms so don't rot
Difficult to get rid of plastics if you bury them in a landfill site
When plastics are burnt, some release gases such as acidic sulur dioxide and poisonous hydrogen chloride
Plastics therefore should be reused as many times as possible by recycling them whenever possible 

Hydrocarbon = contrain hydrogen and carbon atoms ONLY

Hydrocarbons are always held together by covalent bonds, formed when electrons are 'shared'
Both atoms get a full outer shell and the bonds are very strong

ALKANES HAVE ALL C-C SINGLE BONDS

Alkanes are the simplest type of hydrocarbon, they're chains of carbon atoms with 2 or 3 hydrogens attached
Alkanes are SATURATED compounds - only one single covalent bonds between carbon atoms
Won't form polymers as no double bonds to open up
All alkanes have formul : CnH2n+2 

Telling the difference between alkanes and alkenes:

Add substance to bromine water, alkAne won't decolourise the bromine water

ALKENES - hydrocarbons with one or more double bond between carbon atoms
UNSATURATED COMPOUNDS - just means they contain at least one double carbon bond

Covalent bonds are single or double, double covalent bonds are formed when two pairs of electrons are needed to fill their outer shell

Testing for alkenes:
Alkenes react with BROMINE WATER to form a DECOLOURISE liquid
If there are any double bonds they'll react with the bromine, you just add the substance to the bromine and shake it, if it decolourises it's an alkene if it doesn't then it's not

   CnH2n

Crude oil is formed from the buried remains of plants and animals (fossil fuel) over millions of years, with high temperature and pressure, the remains turn to crude oil and can be dug up
CRUDE OIL - mixture of lots of different hydrocrabons
Different hydrocarbons in crude oil are seperated by fractional distillation, oil is heated until it's gas and then the gas enters a fractionating column where a temperature gradient seperates the hydrocrabons

Longer hydrocrabons have higher melting points so they turn to liquids first because the column is hottest at the bottom, shorter hydrocarbons have lower boiling points so they drain out nearer the top

As the size of a hydrcarbon molecule increases:

• Boiling point increases
• Less flammable
• More viscous (doesn't flow so easily)
• Less volatile (doesn't evaporate so easily)

Types of bonds in crude oil:
1) strong covalent bonds between carbon and hydrogen within each hydrocarbon molecule
2) intermolecular forces of attraction between different hydrocarbon molecules

When crude oil is heated, molecules are supplied with extra energy making the molecules move around more, eventually a molecule will have enough energy to overcomes the intermolecular forces and breaks away
Covalent bonds are much stronger so they DON'T break

Big molecules have higher boiling points than small molecules 

CRACKING - splitting up long-chain hydrocarbon - form of THERMAL DECOMPOSITION
Turns ALKANE molecules into smaller ALKANE and ALKENE molecules which are more useful
Involves breaking strong covalent bonds so needs lots of heat and a catalyst
Longer molecules from fractional distillation are cracked into smaller molecules as they're more in demand

1) Vaporised hydrocarbons are passed over powdered catalyst at about 400c - 700c
2) Aluminium oxide is the catalyst used, long-chain molecules split apart on the surface

Cracking - helps match supply and demand
 

Crude oil provides energy needed for vital things in life, as Earth's population increases and countries become mre developed, more fossil fueld are burned to provide electricity for homes and manufacturing
Crude oil supplies are LIMITED and NON-RENEWABLE, new reserves are normally found but we will run out
Means we have to think about alternative fuel (nuclear or wind etc), some people think we should stop using oil for fuel and keep it for making plastics and other chemicals

OIL = POLITICAL and ENVIRONMENTAL PROBLEMS

POLITICAL :
- As stock decreases, prices will increase, countries with big stock could stop selling it and keep for own use
-Countries with most oil will have power over other countries (choose who does and doesn't get supply)...wars?
-Harder for countries, like UK, without oil and gas to get hold of it

ENVIRONMENTAL:
-Oil tanker crashes lead to huge amounts of crude oil lost in the sea, creates oil slicks, killing wildlife
-Oil covers sea birds feathers and stops them being waterproof, die of cold, or can't fly
-Detergents are used to clean up oil slicks but can still harm wildlife, toxic to marine creatures like fish

CHOOSING THE BEST FUEL:
T - toxicity
E - energy value
A - availability 
C - cost
U - use, easy or hard
P - pollution
S - storage

COMPLETE COMBUSTION - LOTS of OXYGEN - bunsen burner OPEN - BLUE flame

hydrocarbon + oxygen --> carbon dioxide + water

Releases lots of energy and only produces two harmless products
Gas burns with clear BLUE flame

CH4 + 2O2 --> 2H2O + CO2

Showing a fuel burns to give CO2 and H2O:
Water pump draws gases from burning hexane through apparatus, water collects in cooled U-shape tube, can show it's water by boiling point, limewater turns milking showing that CO2 is present

INCOMPLETE COMBUSTION - NOT ENOUGH OXYGEN - bunsen burner CLOSED - ORANGE flame 

hydrocarbon + oxygen --> carbon monoxide + carbon dioxide + carbon + water

CARBON MONOXIDE - colourless, odurless, poisonous gas - very dangerous
People die due to faulty gas fires and boilers filling the room with carbon monoxide
Want lots of oxygen when you're burning fuel

4CH4 + 6O2 --> C + 2CO + CO2 + 8H2O 

PHASE 1 - volcanoes gave out steam and CO2

Earth's surface was orginally molten, eventually it cooled and formed a thin crust but volcanoes continued to erupt releasing CARBON DIOXIDE, STEAM and AMMONIA
The EARLY ATMOSPHERE was MOSTLY CO2 and WATER VAPOUR
Very little oxygen

PHASE 2 - green plants evolved and produced oxygen

CARBON DIOXIDE DISSOLVED in oceans
Green plants REMOVED CARBON DIOXIDE when photosynthesising and PRODUCED OXYGEN
Amount of O2 increased and CO2 got trapped in sedimentary rocks and fossil fuels
NITROGEN was put into the atmosphere by AMMONIA REACTING WITH O2 and RELEASED BY DENITRIFYING BACTERIA
NITROGEN isn't very reactive so N2 in ATMOSPHERE INCREASED because it was made but not broken down

PHASE 3 - ozone layer allows evolution

Buildup of oxygen in the atmosphere killed off ealy organisms that couldn't tolerate it
Oxygen also allowed evolution of more complex organisms 
Oxygen created the ozone layer which blocked harmful IR rays from sun
Virtually no CO2 left anymore

PRESENT COMPOSITION OF ATMOSPHERE:
78% Nitrogen
21% Oxygen
0.035% Carbon Dioxide

Carbon - constantly recycled 
Respiration, combustion and decay add carbon dioxide to the atmoshpere
Photosynthesis removes carbon dioxide from the air

Human activity - increases amount of carbon dioxide
More people means more energy used in lighting, heating, cooking, transport etc so more CO2 burnt 
More people also means more deofrestation because houses are needed, less CO2 taken out of atmosphere 

When fossil fuels are burned CO2 is released as well as sulfur dioxide
Nitrogen oxide is created when nitrogen and oxygen react in the air caused by the heat of burning
When sulfur dioxide and nitrogen mix with cloud, they form sulfuric acid and nitric acid, acid rain

Acid rain causes lakes to become acidic and many plants and animals die as a result, acid rain kills trees and damages limestone buldings and stone statues
Nitrogen oxide also causes photochemical smod which is a type of air pollution caused by sunlight acting on oxides of nitrogen, the oxides combine with oxygen to produce ozone (O3)
Ozone (O3) causes breathing difficulties, headaches and tiredness

Carbon monoxide can prevent lood from carrying oxygen around the body
Carbon monoxide is formed when petrol or diesel in car engines is burnt without oxygen

Builup of pollutants can lead to unhealthy lives of animals, plants and humans
Catalytic converters on moto vehicles reduce the amount of carbon monoxide and nitrogen oxides released
The catalyst is normally a mixture of PLATINUM and RHODIUM

carbon monoxide + nitrogen oxide --> nitrogen + carbon dioxide
2CO + 2NO --> N2 + 2CO2

CATALYTIC CONVERTER - helps exhaust gases react to make less dangerous gases